The R-T-B based magnet (R is a rare earth element, and T is Fe or Fe with part of which has been replaced with Co, and B is boron) having the tetragonal compound R2T14B as the main phase is known to have excellent magnetic properties and has been a representative permanent magnet with high performance since it was invented in 1982 (Patent document 1: JP59-46008A).
The R-T-B based magnet in which the rare earth element R is formed of Nd, Pr, Dy, Ho and Tb is preferable as a permanent magnet material with a big magnetic anisotropy field Ha. Among them, the Nd—Fe—B based magnet having Nd as the rare earth element R is widely used in people's livelihood, industry, conveyer equipment and etc. because it has a good balance among saturation magnetization Is, curie temperature Tc and magnetic anisotropy field Ha, and is better in resource volume and corrosion resistance than R-T-B based magnets with other rare earth elements. However, the Nd—Fe—B based magnet has a big absolute value of the temperature coefficient of the residual flux density. Especially, it can only have a small magnetic flux under a high temperature above 100° C. compared to that under room temperature.